Rotary machines are utilized in a variety of power generation and energy conversion applications. A rotary machine in general may include a stationary or fixed member enclosing a rotatable member. The rotatable member can be actuated by the force of a fluid such as water or hot gases. In a conventional rotary machine, such as a hydraulic turbine, the rotatable member includes turbine blades which are circumferentially surrounded by a stationary shroud.
A clearance is provided between the shroud and tips of the turbine blades to avoid any damage to the turbine blades and the shroud walls during operation of the turbine. A large clearance may lead to inefficiency of the turbine while a small clearance may increase the chances of the blades hitting the shroud during operation, resulting in damage to the shroud and/or the blades. Therefore, a uniform clearance has to be maintained between the turbine blades and the shroud. Continuous monitoring of the clearance and maintaining a uniform clearance is necessary for efficient and reliable operation of the rotary machine.
One of the existing solutions uses a capacitive sensor for clearance monitoring in rotary machines. The capacitive sensor determines the clearance between the turbine blades and the shroud. Additionally, the sensor may provide this information to a device or an operator to take appropriate actions and achieve uniform clearance. Typically, a long drilling machine is used to drill a hole through the concrete and/or metal of the shroud wall to install the sensor. The sensor can then be threaded into this hole. However, the installation of the sensor by drilling a hole is difficult, time consuming, and can weaken the shroud wall. Other methods utilize sensor assemblies that can mount to the shroud wall, but the sensor may protrude from the shroud wall due to the thickness and the inflexible design of the sensor. The inflexible design is attributed to manufacturing of the sensor on a rigid substrate and on the sensor housing. Mounting a thick and inflexible sensor into an already narrow gap between the turbine blade and the shroud wall may increase the risk of the turbine blade striking and damaging the sensor. Furthermore, if the gap between the turbine blade and the shroud is increased to accommodate the thickness of the sensor, the gap may be too large for optimum performance of the turbine.
FIG. 1 is a schematic representation of an example prior art turbine apparatus 100. The prior art turbine apparatus 100 is a vertically arranged hydraulic turbine such as a Kaplan turbine 100 that may be used in a high-flow, low-head power production. The Kaplan turbine 100 is an inward flow reaction turbine, which means that the pressure of the working fluid changes with its passage through the Kaplan turbine 100 and thus produces energy. The Kaplan turbine 100 includes an inlet 102, which may be a scroll-shaped tube that wraps around wicket gates 104 of the Kaplan turbine 100. Water may be directed tangentially, through these wicket gates 104, and further spirals on to turbine blades 106, causing the turbine blades 106 to spin. The turbine blades 106 act as a rotatable member in the Kaplan turbine 100. Also, shroud walls 108 that act as the stationary member in the Kaplan turbine 100 circumferentially surround the turbine blades 106. The shroud walls 108 are usually made up of steel surrounded by concrete that may be 1 to 3 meters thick. Further, the Kaplan turbine 100 includes an outlet 110 that may be a specially shaped draft tube that helps to decelerate the water and recover kinetic energy.
Ideally, the space between a tip of the turbine blades 106 and the shroud walls 108 should be zero (hereinafter referred to as zero clearance). The clearance is a space through which some water may pass without hitting the turbine blades 106. As a result, the operation of the Kaplan turbine 100 may be inefficient. However, practically the zero clearance has some limitations as even a slightest vibration in a turbine shaft may cause the turbine blades 106 to hit the shroud walls 108. Thus, a small and uniform clearance is essential between the turbine blades 106 and the shroud walls 108. Typically, a clearance of about 5 to about 10 millimeters may be maintained to achieve relatively efficient working and operational safety of the Kaplan turbine 100.
Therefore, a continuous monitoring of the clearance between the shroud walls 108 and the turbine blades 106 is required for efficient and reliable operation of the Kaplan turbine 100. Any number of sensors may be used in the Kaplan turbine 100 to monitor clearance between the shroud walls 108 and the turbine blades 106. For this purpose, as shown in the FIG. 1, a sensor 112 may be used in the Kaplan turbine 100. The sensor 112 may be a capacitive water gap sensor. Moreover, the capacitance sensors can also be used to measure presence, density, thickness, and location of other conducting members. However, one of the drawbacks associated with the capacitive sensor 112 that is mounted in the hole drilled through the shroud, as shown in FIG. 1, is that it usually requires the removal of extra metal around the drilled hole, otherwise the probes will be “side loaded” and their effective range will be reduced. Typically, a long drilling machine may be used to drill a hole 114 through concrete and/or metal of the shroud walls 108 to install the sensor 112. The sensor 112 may then be threaded into this hole 114. The sensor 112 may also be covered with a sealant.
The Kaplan turbine 100 may further include sensor leads 116 such as a set of cables that connect the sensor 112 to a measurement conversion and/or read-out device. As shown in the FIG. 1, the device may be a monitoring system 118 that receives monitored information from the sensor 112. The monitoring system 118 may then perform necessary actions using the monitored information to achieve a uniform clearance between the turbine blade 106 and the shroud walls 108. The uniform clearance may lie within a pre-defined minimum and maximum range specified by an operator of the Kaplan turbine 100.
FIG. 2 is a schematic representation of another example prior art system 200 for clearance monitoring. As shown in the FIG. 2, a clearance 202 is provided between a turbine blade 204 and a shroud surface 206 (a portion of shroud walls 214). In this example prior art system 200, a sensor 216 is installed along a sidewall of the shroud surface 206. The sensor 216 may monitor the clearance 202 between the shroud surface 206 and the turbine blade 204. The sensor 216 may also be covered with a sealant that may not interfere during the clearance measurement.
The example prior art system 200 may further include sensor leads 208 that connect the sensor 216 to a monitoring system 210 that receives monitored information from the sensor 216. The sensor leads 208 may be a set of cables that may route through an exit hole 212, located below the turbine blade 204, to the monitoring system 210. The functioning of the monitoring system 210 may be same as the functioning of the monitoring system 118 described earlier in conjunction with the FIG. 1.
Each of the prior art clearance measurement systems, as explained above in conjunction with FIGS. 1 and 2, suffer from installation difficulties, or from non-optimal operation of the turbine. For example, the thickness and rigidity of the sensor 206 in FIG. 2 requires that the gap 202 must be greater than the thickness of the sensor 206 to avoid damaging the sensor. Therefore, if the sensor 206 is too thick, the operator will not install the sensor, and it is highly unlikely that the turbine blades would be trimmed to accommodate a thick sensor. If the thick sensor does manage to fit in the gap between the turbine blades and the shroud wall, the gap clearance will be reduced, and there will be an increased risk of impact.
Accordingly, there is a need for systems, methods, and apparatus for monitoring clearance in a rotary machine. Additionally, there is a need for systems, methods, and apparatus for monitoring clearance between a rotatable member and a stationary member in a rotary machine.